Thin film transistor (TFT) liquid crystal display (LCD) devices, as flat-panel display devices, are used increasingly in high-performance display applications due to their advantages such as small size, low power consumption, no radiation, and relatively low manufacturing cost. As display devices become bigger and bigger in size, it is required that display devices be manufactured with higher resolution and better high frequency driving performance. It is thus required that a TFT should have a high mobility and high performance. In order to improve electron mobility in a semiconductor active layer, the semiconductor active layer is usually made of a semiconductor oxide material (e.g., IGZO, Indium Gallium Zinc Oxide), whose electron mobility is dozens of times of that of an amorphous silicon layer. In prior arts, there are mainly two types of array substrates using IGZO as a semiconductor active layer: top gate IGZO TFT structure and etch stop layer (ESL) IGZO TFT structure.
FIG. 1a schematically shows structure of a top gate IGZO TFT in a prior art when it is viewed from a normal direction of a substrate. FIG. 1b schematically shows a cross-section of the top gate IGZO TFT in FIG. 1a. As shown in FIG. 1a, a gate 11 partially overlaps an IGZO active layer 12; a drain 13 and a source 14 also overlap the active layer 12; and the drain 13 and the source 14 are respectively provided on upper and lower sides of the gate 11 and are connected with the IGZO active layer 12 through a first via hole 15 and a second via hole 16. Because the gate 11 does not overlap the drain 13 and the source 14, a stray capacitance produced by the gate 11 is very small. For this reason, top gate IGZO TFT structures have wide applications in the technical field of display panels.
FIG. 2a schematically shows structure of an ESL IGZO TFT in a prior art when it is viewed from a normal direction of a substrate. FIG. 2b schematically shows a cross-section of the ESL IGZO TFT in FIG. 2a. As can be seen from FIGS. 2a and 2b, an IGZO active layer 22 is provided inside a gate 21; a drain 23 and a source 24 respectively overlap the IGZO active layer 22; and the drain 23 and the source 24 are provided respectively on upper and lower parts of the IGZO active layer 22 and are connected with the IGZO active layer 22 through a first via hole 25 and a second via hole 26. In the TFT structure, an etch stop layer 27 is configured to be a protective layer of the IGZO active layer, for protecting the IGZO active layer from a metal etching solution used in a subsequent procedure. The TFT structure has an excellent electrical property. Therefore, ESL IGZO TFT structures also have wide applications in the technical field of display panels.
Unfortunately, when a top gate IGZO TFT structure or an ESL IGZO TFT structure in the prior arts is used in a GOA circuit or in other circuits, a channel of the TFT has to be designed with a large width, as a consequence of which, the TFT occupies a large space, which is not conducive to a narrow-bezel design of a display panel.